Batteries are essential for the portability of wireless terminals, for example cellular phones and other portable communication devices. Rechargeable batteries in cellular phones and other portable communication devices, such as NiCd, nickel-metal hydride (NiMH), Lithium-ion, lithium iron phosphate (LiFePO4), and Lithium-Polymer batteries, may be recharged with household alternating current (AC) power coupled through a voltage reduction transformer, an alternating-to-direct current converter, and appropriate battery monitoring and charging circuits. They may also be recharged with a 12-volt cigarette lighter socket provided in an automobile coupled through a DC voltage reduction circuit and appropriate battery monitoring and charging circuits. They may also be recharged using solar cell, windmill, another battery or any other suitable power source. However, typical battery chargers do not provide a reliable estimate of the remaining charging time needed until the battery is charged to its maximum capacity.